Field of the Invention
The present invention relates to an apparatus for explosively severing tubular members and more specifically to an apparatus for severing tubular members below a body of waer, such as, for example, an offshore rig platform pile.
During offshore drilling and production operations, it is sometimes necessary to move a platform to a different location, retrieving as much of the equipment as possible. An offshore platform is usually supported by a number of piles which extend from the platform downwardly through the body of water and below a mudline. It is usually there, below the mudline, that the piles have to be severed in order to the platform to be transported to a new, preselected location.
At present, the most commonly used explosive severing method utilizes a bulk explosive which is delivered to a level below the mudline through the interior of the pile, where it is detonated to produce an explosive charge. The results of such explosion are extremely unsatisfactory, since the unfocused charge not only creates signficant shock waves which create hazardous conditions for sea life, but the bottom of the so severed pile becomes flared, which makes it difficult for operators to remove the severed portion through the jacket which surrounds the pile circumferentially.
The currently used bulk explosive methods utilize approximately 60 lbs. of explosive or 1 lb. per diametric inch of the pile plus 10% or 15% of additional explosive.
Other devices and methods utilized to severe piles below the mudline include the use of a 2 point explosive, wherein a circular body carries a pair of diametrically positioned explosive units for detonating them at a point where the severing of the pile is desired.
The use of such an explosive also creates problems, one of the problems being a noncomplete severance of the pile or significant shock waves, which consequently effects the sealife.
There are also a number of methods which utilize ring-shaped explosive charges wherein the detonation is initiated at one point of the circle, allowing the detonation to spread out through the circle in a sporadic manner.
None of the above-noted devices can be utilized to create a focused charge which will accomplish severing of the pipe in the beneficial manner afforded by the present invention. It is therefore an object of the present invention to provide an apparatus wherein detonation is accomplished to create a focused charge, so that the pile or a tubular member is severed at an exact chosen location, without creating flare to the pile or unnecessary excessive shock waves affecting the sealife.
It is a further object of the present invention to provide an apparatus for creating a focused, uniform explosion for severing tubular objects wherein the detonation occurs at a plurality of points substantially simultaneously adjacent to the inner periphery of the tubular member being severed.